Fix WiFi reconnect bugs, negative-temp rounding, and stale docs

- Clear WIFI_CONNECTED_BIT on disconnect so wifi_is_connected() stops
  reporting a link that is gone; the weather task's reconnect path was
  dead code without it.
- After the 8 fast retries are spent, retry every 30s via an esp_timer
  forever instead of giving up until power cycle. FAIL_BIT now only
  unblocks the boot-time wait and is cleared on reconnect.
- Start the weather task even when the boot-time connect times out --
  the background retries may still bring WiFi up later. Only an empty
  SSID skips it.
- Round temperatures with lroundf(): the old +0.5f-and-truncate rounded
  toward zero below 0degF (-10.6 displayed as -10).
- Drop the stale single-framebuffer "Partial-mode flush" comment in
  display_rgb.c, fix the README paragraph claiming the bounce buffer is
  disabled (it is enabled and load-bearing), and correct the
  sdkconfig.defaults header to N16R8/16MB.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

main/drivers/display/display_rgb.c

@@ -87,14 +87,6 @@ static const char *TAG = "display_rgb";
 static esp_lcd_panel_handle_t panel = NULL;
 static lv_display_t *disp = NULL;
 
-/*
- * Partial-mode flush: blit the dirty rectangle from a small internal-RAM
- * draw buffer into the single PSRAM framebuffer.
- *
- * Page-flipping two framebuffers instead would be cheaper, but the swap
- * lands mid-scanout on this panel and tears visibly. Copying into one
- * framebuffer that the LCD scans continuously is what the vendor driver does.
- */
 /*
  * Double-buffered flush.
  *

main/main.c

@@ -1,3 +1,4 @@
+#include <math.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -54,7 +55,9 @@ static void weather_update_task(void *arg)
             snprintf(detail, sizeof(detail), "%.0f%% humidity",
                      weather.has_humidity ? weather.humidity : 0.0f);
 
-            ui_update_weather((int16_t)(weather.temp_f + 0.5f),
+            /* lroundf, not +0.5f-and-truncate: the latter rounds toward zero
+             * below 0°F, turning -10.6 into -10. */
+            ui_update_weather((int16_t)lroundf(weather.temp_f),
                               weather.has_humidity ? detail : "Outdoor");
 
             wifi_get_status(line, sizeof(line));
@@ -83,7 +86,7 @@ void app_main(void)
      */
     const esp_err_t wifi_err = wifi_init_sta();
     if (wifi_err != ESP_OK) {
-        ESP_LOGE(TAG, "WiFi failed -- continuing, weather will be disabled");
+        ESP_LOGE(TAG, "WiFi not up yet -- weather starts when it connects");
     }
 
     /* LVGL core must exist before the display and touch drivers register
@@ -114,15 +117,22 @@ void app_main(void)
     vTaskDelay(pdMS_TO_TICKS(100));
     ESP_ERROR_CHECK(backlight_set(255));
 
-    if (wifi_err != ESP_OK) {
-        ui_set_status("WiFi: failed");
+    if (wifi_err == ESP_OK) {
+        char status[96];
+        wifi_get_status(status, sizeof(status));
+        ui_set_status(status);
+    } else if (wifi_err == ESP_FAIL || wifi_err == ESP_ERR_TIMEOUT) {
+        /* The event handler keeps retrying in the background; the weather
+         * task polls wifi_is_connected(), so start it anyway rather than
+         * permanently disabling weather because boot raced a slow AP. */
+        ui_set_status("WiFi: connecting...");
+    } else {
+        /* No SSID configured (or setup failed outright) -- nothing will ever
+         * connect, so there is no point starting the weather task. */
+        ui_set_status("WiFi: not configured");
         return;
     }
 
-    char status[96];
-    wifi_get_status(status, sizeof(status));
-    ui_set_status(status);
-
     if (weather_init() != ESP_OK) {
         ui_set_status("Weather: no API credentials");
         return;

main/wifi/wifi_manager.c

@@ -4,6 +4,7 @@
 #include "esp_log.h"
 #include "esp_netif.h"
 #include "esp_system.h"
+#include "esp_timer.h"
 #include "esp_wifi.h"
 #include "freertos/FreeRTOS.h"
 #include "freertos/event_groups.h"
@@ -18,10 +19,20 @@ static const char *TAG = "wifi_manager";
 #define WIFI_FAIL_BIT      BIT1
 #define WIFI_MAX_RETRIES   8
 #define WIFI_CONNECT_TIMEOUT_MS 30000
+/* After the fast retries are spent, keep trying at this interval forever --
+ * this is a wall appliance, so an AP outage must not require a power cycle. */
+#define WIFI_RECONNECT_DELAY_MS 30000
 
 static EventGroupHandle_t s_wifi_event_group = NULL;
+static esp_timer_handle_t s_reconnect_timer = NULL;
 static int s_retry_count = 0;
 
+static void reconnect_timer_cb(void *arg)
+{
+    ESP_LOGI(TAG, "Slow reconnect attempt");
+    esp_wifi_connect();
+}
+
 static void wifi_event_handler(void *arg, esp_event_base_t event_base,
                                int32_t event_id, void *event_data)
 {
@@ -31,18 +42,28 @@ static void wifi_event_handler(void *arg, esp_event_base_t event_base,
     }
 
     if (event_base == WIFI_EVENT && event_id == WIFI_EVENT_STA_DISCONNECTED) {
+        /* Without this, wifi_is_connected() keeps reporting true after a
+         * drop and callers never notice the link is gone. */
+        xEventGroupClearBits(s_wifi_event_group, WIFI_CONNECTED_BIT);
+
         /*
-         * Only give up after a bounded number of retries. Signalling failure
-         * on the first disconnect (as this previously did) meant a single
-         * transient drop was reported as a hard failure.
+         * A bounded burst of immediate retries covers transient drops;
+         * signalling failure on the first disconnect (as this previously did)
+         * meant a single blip was reported as a hard failure. Once the burst
+         * is spent, fall back to a slow periodic retry instead of giving up:
+         * FAIL_BIT only unblocks the boot-time wait in wifi_init_sta().
          */
         if (s_retry_count < WIFI_MAX_RETRIES) {
             s_retry_count++;
             ESP_LOGW(TAG, "Disconnected, retry %d/%d", s_retry_count, WIFI_MAX_RETRIES);
             esp_wifi_connect();
         } else {
-            ESP_LOGE(TAG, "Giving up after %d retries", WIFI_MAX_RETRIES);
+            ESP_LOGW(TAG, "Still down after %d fast retries; retrying every %d s",
+                     WIFI_MAX_RETRIES, WIFI_RECONNECT_DELAY_MS / 1000);
             xEventGroupSetBits(s_wifi_event_group, WIFI_FAIL_BIT);
+            esp_timer_stop(s_reconnect_timer);
+            esp_timer_start_once(s_reconnect_timer,
+                                 (uint64_t)WIFI_RECONNECT_DELAY_MS * 1000);
         }
         return;
     }
@@ -51,6 +72,7 @@ static void wifi_event_handler(void *arg, esp_event_base_t event_base,
         const ip_event_got_ip_t *event = (const ip_event_got_ip_t *)event_data;
         ESP_LOGI(TAG, "Got IP: " IPSTR, IP2STR(&event->ip_info.ip));
         s_retry_count = 0;
+        xEventGroupClearBits(s_wifi_event_group, WIFI_FAIL_BIT);
         xEventGroupSetBits(s_wifi_event_group, WIFI_CONNECTED_BIT);
     }
 }
@@ -67,6 +89,12 @@ esp_err_t wifi_init_sta(void)
         return ESP_ERR_NO_MEM;
     }
 
+    const esp_timer_create_args_t timer_args = {
+        .callback = reconnect_timer_cb,
+        .name = "wifi_reconnect",
+    };
+    ESP_ERROR_CHECK(esp_timer_create(&timer_args, &s_reconnect_timer));
+
     esp_err_t ret = nvs_flash_init();
     if (ret == ESP_ERR_NVS_NO_FREE_PAGES || ret == ESP_ERR_NVS_NEW_VERSION_FOUND) {
         ESP_ERROR_CHECK(nvs_flash_erase());